The Japanese version of the Toyota booking engine is actually pretty easy to navigate with auto-translate on Google Chrome:

https://rent.toyota.co.jp/rakuraku/step1.aspx

'P' is the standard category, and you get discounts if you don't select the actual car type within the category. Your booking email is in Japanese, of course, but I found that rather helpful in getting the car sorted out (we rented from Kanazawa station).

Otherwise, Nissan have an English booking engine:

https://nissan-rentacar.com/english/

Our experience with Toyota was great - very friendly and helpful counter staff at Kanazawa (they had a crib sheet for English-speaking customers, as well as Google Translate on hand on their iPads). We were allocated something I've never heard of before, which would best be described as two boxes welded together, but it drove really well - and they threw in English GPS for free (I generally don't use GPS, but it was handy in a couple of places). Insurance was the same system as we have here, so no confusion there.

We'd got it to explore the Noto Peninsula and Shirakawa-go, on the way to Takayama (Gifu), to pick up the Hida train (really lovely journey) down to Nagoya for Kyoto.

Parking was pretty easy - you do need to hone your reversing-into-spaces skills if you want to use your standard back-street parking spots (there seemed to be very little on-street parking, but plenty just-off-the-street spaces where you reverse in, a wheel-blocker raises up, and you pay to release it).

The expressways we used were easy to figure out - happily didn't come across any ETC-only tolls (checked this out on Google Maps in advance).

Getting petrol was a bit of an experience, being unable to read Japanese - it seemed to mostly work on the basis that you guess how much money to put in for a particular pump, put it into a machine (that serves multiple pumps), but you'll get some change if you fill less than the amount you put it. I found that standing round looking endearingly baffled inevitably had someone over to help me out, followed by profuse thanks.

In general, driving was pretty easy and laid-back. Took a while to get used to traffic lights on such a high level, and to get the tempo of just how much you exceed the (really rather low) speed limits by out of town. But it seemed pretty polite and relatively competent where I was.

Returning the car was fine, too - very quick, very easy. Very good experience, and I'd rent from them again.